Acoustic device with sonorous membranes



April 14, 1931. M. BERNARD 1,800,591

ACOUSTIC DEVICE WITH SONOROUS MEMBRANES Filed July 23, 1929 .FLSgL INVENTOR MARGEL BERNARD ATTORNEY Patented Apr. 14, 1931 UNITED STATES PATENT OFFICE.

App cat on led. my 23. 1. 2% Easel lie. .94% are in Item Num e 5 2% The present invention is concerned with devices which transmit or receive sounds and are equipped with a vibrating membrane, such as intensifier telephones, phonographs,

6 micro hones, etc. It applies articularly to such evices'which are provi ed with a" vibrating membrane oflarge dimensions,

'The'subjest of this invention is a novel method of attaching the vibratingmembrane 10 which provides'among other advantages the tensional forces assuring the rigidity'of the membrane as well as the elastic forces necessary to reestablish the, membrane in its position of rest,

16 Theinvention will be more clearly under stood byreferring to the attached figures and to the, description pertaining thereto which illustrate, byway of an arbitrary example, a method of embodying its principle.

90 In the drawing Figure 1 is a sectional view 9f an approved form'of my invention;

Fi ure 2 is a force diagram for the struc: ture 1 lustrated by Figure '1;

Figure 3 is a plan view ofthe spring member disclosed in Figure 1 Figure 4 is a sectional view of a modification of my invention; and

Figure5 is a lan view of the modification ustra ed. by i gu e 4- Y e cone shaped t pan or membrane 1 is provided at its periphery with a cylindrical part or brim 2 which may be either attached to the tympan by gluing or otherwise 86 or obtained directly by a corresponding shaping of the material which constitutes the body of the tympan. A spring 3 is caused to exert a pressure against the internal surface of the cylindrical brim 2. This spring is 40 made of a thin strip of material, for instance, sheet metal, which has been bent in such a way that it will when compressed by its insertion under the brim of the tympan, exert a force inclined to the axis of the latter. Figure 2 shows that this force F may be resolved into two components, i. e. a radial force f and an axial force f,. The radial force f contributes to the rigidity of the membrane by tensioning it while the axial force f assists in overcoming the opposing action of the driving motor until the tympan is in a state of equilibrium.

In orderto acoustically isolate the tympan from the sprin a layer of inert material such as felt, in ia-rubber moss, cotton wadding, etc., is interposed between the two members. In the example illustrated by Figure 1 a band of felt 4-has been folded over the cylindrical brim of the tympan for this purpose.

Springs such as 3 are placed at certain intervals along the periphery of the tympan. Their number may vary and, if desired, they may be made of a single metal sheet suitably cut and shaped. Figure 3 illustrates such a member which consists of the metal crown 5 and four depending springs 3. The spring 3 of Figure 1 may be considered as a section taken'in an axial plane a b of Figure 3. The metallic crown is easily fastened to the support (l or the apparatus by means of any of the known methods. The support 6 may an even surface such as a thin board to which the straight part of the crown is attached in such a way as to form a circular opening calculated to freely propagate the sounds emitted by the tympan. The driving motor, of any type, may rest on the same support by means of arms or brackets suitably arranged accordin to known methods. The notches I or the metal crown, or, in a general way, the gaps between the springs 3 should preferably be closed in such away as not to impede the lay of the springs f. i; by means of a flexible and of felt or cloth. 3?

It is equally possible to build a loudspeaking devise with two membranes constructed according to this invention, the membranes being of equal or different size, placed with their peaks towards each other and operated by the same driving motor.

My copending application, Serial No. 869,fi76, describes and claims the/structure disclosed by Figures 1 to 3..

It will now be possible to scrutinize certain details of construction and certain modifications which assist in improving the reproduci'ng qualities of the device.

First, as faras the conical membrane itself 1 is concerned, it is preferably built of paper qualities, drawing paper of small texture of a. compressed thickness of 0.20 to 0.30 mm. Secondly, the cone should have a relatively small angle at its peak, say. 90 to 100".

Thirdly, the cone should be reinforced in its middle part. A simple expedient to effect such a reinforcing consists ofseveral layers of paper glued on top of each other. A good result is obtained by gluing to one side of the. cone a small cone 20 mm. long, measured along its side, and to the other side-a frustrated cone 15 mm. long, also measured along the side of the main cone. Thetwo reinforcing pieces may either cover each other'or may be separated or follow each other immediately along the side of the membranecone. I Y a i 4 V 'Fourthly, in regard to supporting the cone along its periphery the following procedure may be employed: The edge of the cone is covered with a band of a substance forming an elastic and soft mat wrapped around the edge and preferably glued to the paper. The resulting cushion isforced between the teeth of a crown which is derived from the one 7 previously described but, differs from the latter in that its teeth are bent so that they come to lie alternately on the inside and the outside of the cone and exert no pressure whatever on the cushion. The whole arrangement constitutes avery soft suspension of the tympan;

Figure 4 is a cross section and Figure 5 is a plan view with part section of a tympan and its support, all in accordancewith the invent-lOII if I V 3 :In these figures,'1 isa conical membrane of large dimensions'made of light but rigid paper corresponding to the-above given specitonwadding, wool, india-rubber moss etc., 7

is wrapped around the edge and preferably glued-to the cone. Thus linedthe edge. is forcedbetween the teethS, 3' which are cut which is connected to the latter at the apex;

The invention is obviously susceptible to numerous variations according to the nature of the materials employed, the dimensions of the movers, thenature of the acoustic devices to which it is applied (loudspeakers,

microphones, phonographic .difiusers or reproducers, etc.) the formof the membranes (straight membranes, membranes which are unsymmetrical relati'veto the point of at tachment, etc.).

I claim: o

1. An acoustic device comprising a conical diaphragm, a layer of soft material around the edge of said diaphragm and means engaging said layer of soft material for supporting said diaphragm, saidqmeanscome prising a member provided with a plurality of teeth which are alternately bent, the edge of said diaphragm being inserted between said teeth so that adjacent'teeth lie on op posite sides of said diaphragm.

; 2. An acoustic device comprising a conical diaphragm, a stiffening cone secured to theoutside of said conical diaphragm at its apex, a stiiiening bandsecured to the inside of said conical diaphragm, a layerof soft material secured to each side of said conical diaphragm at its edge, said stiffening band being located between said stiffening cone and .said'layer of soft material, and means for-supporting said diaphragm, said means comprising a crown provided with a plurality of teeth adapted to engage the layers 'of soft'material at the edge of said diaphragm, the edge of said diaphragm being'inserted between said teeth so that adjacent teeth are on ,op-

posite sides of said diaphragm; V v

3. a An acoustic device comprising a conical diaphragm, a mass of cotton disposed around the edge of said diaphragm, a supporting member, and a toothed member secured to said supporting member, said mass of cotton on'the edgeofsaid diaphragm being inserted between the teeth of said toothed member. 7

MAR-GEL vBERNARD.

from a rigid" crown 5 of a conical shape, the

successive teeth being slightly bent alternately one-way or the other from the surface of the original cone which has the same peak angle as that of the paper cone. The crown 5 is attached to the support 6 of the tympan by means of screws 9. The crown may be 

